Inside here, you have a folder for each SWEP. If you want to add scripted weapons or scripted entities to the game, you can add a folder inside the Lua folder called 'weapons'. If you have a basic script that you just want to run when you start the game, you should put it in the autorun folder. If you want the script to only execute on CLIENT machines, you must do the same with a folder called 'client.' If you want the script to only execute on the SERVER machine, you must create a folder called 'server' and put the scripts in here. Inside the autorun folder, every Lua script will be executed when the game starts. If you don't see an autorun folder, create one now. Inside here, you should see 4 folders: 'includes', 'postprocess', 'vgui' and 'autorun'. In here, you will find several folders which you will probably be familiar with - such as the addons folder and the maps folder. Navigate to steam/steamapps//garrysmod/garrysmod. So, you have written your first basic script, but where the heck do you put it to make it work? Well, first let's examine the Garry's Mod file and folder structure.

Gmod file location finder